


Aurelian Thorns

by Lyre (Lyrecho)



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: (The Author Does What She Wants), Alternate Universe - Canon Divergence, Author Has Not Completed All FE3H Routes, Author Writes Her Own Lore, Become As Family, Like VERY Not Canon, Multi, No Longer A Joke Fic, Started As A Joke Fic, The Dilf(ix it) Fic, at all, what's a canon
Language: English
Status: In-Progress
Published: 2019-10-28
Updated: 2019-10-28
Packaged: 2021-01-05 14:44:46
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 3,115
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21210272
Author URL: https://archiveofourown.org/users/Lyrecho/pseuds/Lyre
Summary: When Byleth Eisner is offered (coerced into, really) a teaching position at Garreg Mach, they're expecting a few things: to be constantly on guard, to fail at teaching their students anything, and to have no one to rely on but their father.What they'renotexpecting is to be wrong.





	Aurelian Thorns

**Author's Note:**

  * For [KlonoaDreams](https://archiveofourown.org/users/KlonoaDreams/gifts).

> this fic started as a joke about dilfs in the bread and bitter discord server; of course, since we're all a bunch of writers, jokes swiftly become actual ideas. specifically, shoutout to my girlfriend noa, for Enabling Me. this one goes out to you, hon.
> 
> specific warning for this chapter: there's a scene of some animal violence (in a fight) that ends with the animals death. the language used isn't overly descriptive, nor is the scene long or particularly graphic, but it is there, so take care of yourself if that's something you can't handle very well <3

_ They have my trust, Seteth, _ Rhea says. _ Let that be enough. _

With anything else, it would be. Rhea is one of the closest remnants of family he can still cling to.

But Flayn is here now, and while doubting Rhea hurts him - stings, a scorpion’s stab of betrayal - he cannot allow any harm to come to her. Cannot even entertain such a risk.

He trusts Rhea, but not even she is infallible. 

If she is to trust blindly, he must take matters into his own hands.

And so, he does.

-x-

“Oh, Goddess.” Jeralt rolls his eyes as someone slides into the seat across from him, and he looks up to see Seteth frowning around the mug of coffee he sips from. “You’re not over this yet? Really? It’s been well over a month.”

Seteth’s frown, if you can believe it, deepens. “I would think that, as a mercenary, you would know all too well the risk of letting your guard down too soon.”

“I also know well the risk of never letting it down at all,” he says bluntly. “If you’re not careful, those wrinkles won’t go away, you know.”

A hand automatically reaches up to touch at Seteth’s forehead before the man catches himself and jerks it back with a scowl. Jeralt hides his smirk behind his own mug.

“Is it really that hard to believe I’m not up to anything?”

For a second, just a split second, Seteth’s scowl flickers into - something. “I don’t believe you came here with malicious intent,” he says finally. “But that doesn’t mean I trust you. You came here against your will, after all, and I cannot imagine it is simply fear of the church’s reach that keeps you here. You fled once before in spite of that, did you not?” Seteth leans across the table between them, and his voice drops lower. None of the students loitering around will be hearing his next words, even if they’re actively trying to. “Why did you run, Jeralt? What happened two decades ago that caused you to vanish in the wake of a fire?”

Jeralt resettles in his seat. Leans back, so he’s out of Seteth’s space, since the man shows no signs of moving out of _ his _, anytime soon. Sighs, and ignores Seteth’s last question about as easily as he ignores the anxiety it sparks in him - which is to say, not easily at all, but he manages it. “Things are different now,” he says, and his mind drifts to Byleth - his precious child, all he has left of Lilith, all bundled up in precocious quirks. “I have obligations I can’t run from. Not ever.”

He meets Seteth’s gaze evenly, unflinching.

“I suppose that is something I can understand,” he says finally, and withdraws - a surrender, for now, but Jeralt knows enough to know this is not over. Seteth’s next words prove him right. “Do not think you have convinced me to look away from you.” He stands, and turns to walk away. “Whatever your intentions, know I will allow no harm to come to this monastery.”

Jeralt thinks of his child, the quiet little weirdo, smiling gently at their students and coming to him with their worries. He thinks of Leonie, of how she’d lit up at the chance to learn from him again, when he has the time, so grown up from the last time he’d seen her. Thinks of all the children that flock to his child, needing them in a way he thinks they needed.

“You don’t need to worry about any of that from me,” he says, softly. He isn’t even sure Seteth hears him - the man is almost out of the room at that point.

It’s the truth. Regardless of his feelings towards the church, towards - towards Rhea, he has nothing against these kids, or any of the other people that mill about the grounds.

If trouble comes here, Jeralt knows, it won’t be coming from him. He wishes Seteth would open his eyes for just long enough to see that around his paranoia - figuring out who the real danger is would be a lot easier if they could just _ work together _, instead of him constantly having to argue his innocence. It’s exhausting.

“Are you well?”

Jeralt just about jumps out of his skin. Swallowing a curse, he looks up to see his child staring down at him with a raised brow, arms laden down with a breakfast tray and their long hair pulled back out of their face, for once. A pale pink ribbon shines against the dark of said hair, and he wonders which of their little brats gave it to them.

“I’m fine, kiddo,” he says, and gestures to the seat across from him Seteth had just vacated. “Just thinking deep thoughts.”

Their lips quirk up into a faint smile. “Be sure not to get lost digging too deep in that empty head of yours,” they say archly, and Jeralt retaliates by flicking a blueberry at them. 

They catch it in their mouth, and their smile melts into a smirk.

“Yeah, yeah, laugh it up,” he mutters. “Show all your little students just how much you respect your old man.”

They laugh. After a moment, Jeralt follows suit.

The worry Seteth had caused him is, for at least that brief, shining moment, forgotten.

-x-

“Why do you not like Captain Eisner?”

Seteth does not jump. He’d been aware of Flayn’s presence from the moment she had entered his office - when it’s her, he always is. He knows his constant hyper vigilance around her annoys Flayn to no end, but he cannot help it. His love and worry for her entwine and run too deep for him to stop.

He does, however, bite down the urge to curse. Her question is an annoying one, and he knows this to be true, because Flayn has that pout on her face. The one he cannot find himself ignoring.

“I do not dislike Captain Eisner,” he says. “Flayn, do not be ridiculous.”

“That was not my question, brother,” she says, and it still feels weird to hear her call him that. An itch, somewhere in his mind he can’t reach to scratch. “You do not dislike many things. I asked _ why _ you don’t _ like _ him.”

“I don’t even know the man, Flayn -”

“You are not even trying to change that!” She stomps her foot, and Seteth raises a brow at her. “You met him for all of five seconds and had already made your mind up on him. In the past two months, have you even attempted to hold a conversation with him that doesn’t end in an interrogation on your part?”

Seteth deftly ignores that question. “Flayn, speak truthfully: why on earth does this bother you so much?”

She fidgets, fingers knotting in her skirt as she looks away. “Professor Eisner lets me sit in on their classes even though I am not a student,” she says quietly. “I like them, very much, and I do not want your - your animosity towards their father driving them off!”

A stab of something deeper than guilt digs in where it hurts. Flayn is the picture of misery, uncertainty twisting the corners of her mouth as she shrinks in on herself. This life of constant vigilance is never what he wanted for his daughter.

“Flayn, you know that is not my intent,” he says. “I simply worry - they are _ suspicious _, Flayn, and no one else is paying them the consideration they deserve.” He stands, and walks over to her; with one hand pulls her in close, with the other, tilts her chin up, so she can meet his eyes and see the truth in them. “I do not doubt their characters, or their intent,” he states clearly. “But that doesn’t mean they haven’t brought darkness into the monastery.”

Darkness, Seteth knows, that has always been there, hidden in nooks and crannies. No institution is perfect. None without corruption, or secrets - and Rhea holds more than most. He does not begrudge her this. He has his own secrets, after all.

He does not even begrudge Jeralt Eisner for his secrets, truthfully - only that whatever it is he and Rhea were tangled up in together persists to risk exploding when his daughter is at ground zero.

“Besides,” he reminds her. “Rhea appointed Professor Eisner herself. They could not be driven off, even should they want to leave.”

Under his hands, Flayn slumps. “That is not very comforting, brother,” she whispers.

-x-

When Flayn goes missing, Seteth’s irregular ambushes stop.

Jeralt would say he’s thankful for it, except he isn’t, if only for the reason _ why _ they’ve stopped. Flayn’s a sweet kid - she doesn’t deserve whatever it is that’s happened to her.

And while all that is terrible enough, watching Seteth become more haggard and unkempt as days and days pass by with no news is one of the more harrowing things Jeralt’s had to see in a while.

Perched on his desk, legs swinging and brushing against his thighs with each pass, his own child shoots Jeralt a concerned look, and he tries not to imagine what he’d be acting like, if Byleth was in Flayn’s place and he in Seteth’s. He doesn’t succeed very well at doing so.

“Dad?” Byleth asks, slow and careful. They are, for whatever reason, dressed in an academy uniform today; skirt and cape pressed neat, hair braided back and tucked under a cap. Under the skirt, they still have those stupid tights on - the ones Jeralt has never been able to convince them to swap out for something more sensible. “Are you...doing okay?”

There’s hesitance in their voice, their eyes; concern and worry shining through right on the surface.

Jeralt has always known his child wasn’t as emotionless as they seemed to others - for them, for whatever reason, that emotion was just buried deep.

Since his return to the monastery, since Byleth had been dragged along with him and started teaching those brats - they’ve been more...open. It’s for that reason alone that Jeralt hasn’t really started to plan a way for them to leave without drawing Rhea’s attention once they’ve fled.

Jeralt sighs. “I’m fine, kiddo,” he says, and resists the urge to stand and knock their cap off so he can ruffle their hair. “I think the atmosphere is getting to everyone now, is all.”

Pensive, Byleth nods. “Do you think we’ll find her?”

For a long moment, Jeralt is silent. 

“I know we’ll find her,” he says eventually.

He doesn’t say _ I don’t think we’ll be finding her alive _.

Byleth smiles, and for once it reaches their eyes. It’s like being clobbered by a miracle. Twenty-one years old, so worldwise, and yet his child will believe anything he says without looking past the surface meaning, simply because he is their father, and they love him. Trust him, totally.

It’s humbling. It’s terrifying.

In this particular case, it’s heartbreaking. A previously unseen tension bunched up along Byleth’s shoulders drains out, with them reassured by Jeralt that Flayn won’t remain lost forever.

Goddess, but sometimes he hates himself.

-x-

Panicked children flooding into his office is not something Seteth can say he particularly enjoys - Annette and Ashe stumble over each other and speak at the same time, and he can barely pick out whatever it is they are trying to tell him - 

\- and then, he hears it; just one word that rings out clearly when all the rest is nonsensical babble. _ Flayn _.

He is gone, and the sharp yelps of the students behind him are just like the dust he leaves in his wake; swiftly forgotten.

He barks orders at knights he passes by in the halls - single-minded as he may be, he isn’t _ stupid _ \- one such knight is Catherine, who widens her eyes and gives him a solemn nod once she understands his message. She says she’ll rally the rest of the knights.

He says they’ll have to meet him down there.

Catherine doesn’t look pleased, but she doesn’t argue, either.

“Be safe,” she says.

“I will,” Seteth promises. “I always am.”

He walks into the tail end of a massacre. He wants, desperately, to take a moment to breathe, but keen eyes spot Flayn, curled up deep in unconsciousness, Ingrid and Mercedes standing guard over her and another girl - older, a slash of red shining bright that Seteth doesn’t have the presence of mind to question on why it seems so familiar. 

He rushes over, and the eyes of the children light up when they see him.

“Sir!” Ingrid calls out, and he doesn’t let his eyes linger on where her bloodied hands, bone white around her lance, are shaking. “We know we should have waited, but - the Professor didn’t want to risk the assailant making off with Flayn, and His Highness agreed - ”

Seteth holds up a hand to halt her words. “You need not explain yourself to me,” he says. “Not right now, at the very least.” Kneeling down to cradle Flayn - feel her breathing, check her pulse - he peers back up at Ingrid and Mercedes both. “You are both unharmed, I trust.”

Ingrid nods firmly. “Quite,” she says. “We haven’t really been involved with the battle...I’m not quite used to fighting at my best on foot, and Professor Byleth didn’t want to risk Mercedes on the frontlines. Not against opponents such as these.”

A little rueful, Mercedes smiles, and shrugs, but Seteth can feel a frown forming.

This new professor of theirs, so young and untested - inexperienced - had previously not shown much reticence towards taking their students headfirst into battle. If they were taking such precautions _ here _…

Dread beginning to pool, Seteth turns his attention from Flayn and actually, fully, takes in the battlefield he rushed into.

Corpses litter the floor, but that isn’t what is important.

Students litter the floor, too - not dead, but unconscious, or scrambling back to their feet. At the center, face twisted in a snarl, eyes wide, Byleth Eisner stands as a second shield for the Prince of Faerghus. Glowing like a sun, pulsing like a heart, a sword of bone cuts the space between them and the mockery of death that comes at them.

He knows that blade. _ He knows that blade _.

The prince is on his feet once more, lance snapped in two but still clearly raring to fight. There’s a panic in his eyes as he struggles against the arms of his retainer that hold him back - “Dedue!” He snarls. “Dedue - the Professor needs us - ”

“No,” Dedue says, firm, but still gentle. “We were told - ordered - to stay back.”

“They’ll die if we don’t help them!”

“And you will die if you do.” 

“_ Dedue - _”

“No, Dimitri.” Byleth Eisner’s voice is just as firm as Dedue’s, and quite a fair bit more harsh. “I have the line. _ Retreat _.”

Some of the tension that had been visible to Seteth in Byleth’s stance bleeds out, the panic in their eyes ebbing. It seems the reminder that they have students ready and willing to recklessly throw themselves into battle for them has given their shaken confidence a second wind.

Byleth’s snarl twists into something else, and they _ move _ in a flow that Seteth can’t help but freeze at, because _ he knows that, too _ \- 

\- The Sword of The Creator flares brighter, and then with a keen that stretches on it whips out like a chain.

Byleth moves like they were born with the sword in their hand; the blade, red hot, slashes for the horse’s legs, not the rider. It completely severs the front two and, while the horse buckles, panicked and pained whinnies ringing out, continues on to severely wound the hind legs, too.

Seteth can do little more than stare. Unconsciously, his grip on Flayn tightens, and he resists the urge to shove her behind him.

He knows well the damage that blade can do. He isn’t quite sure how he feels about seeing it again, except he knows he _ isn’t _ happy.

He knows he is, at least a little, terrified.

The knight in the horned helm apparently agrees with him, because once his horse falls beneath him, he’s quick to abandon the battlefield altogether.

“Sir?” Ingrid whispers. There’s something awed in her eyes as she stares at Byleth Eisner, something equal parts worshipping and frightened. “Is it over?”

_ Is it over, father? Is it over? _

“Yes, child,” he breathes. “It is over.”

-x-

“_ What _ ,” Jeralt snarls, “in the name of the Goddess _ were you thinking _.”

Byleth tries to smile, fails, shrugs, and promptly grimaces in pain. _ A dislocated shoulder _, Manuela had diagnosed, dazed and wounded herself, and had helped Jeralt snap it back into place, but had not wanted to even attempt any sort of healing magic in her state. Mercedes - sweet kid - had offered to cast a few in her place, but Manuela had taken one look at her exhausted countenance and glared at her so fiercely Jeralt wasn’t surprised she’d immediately dropped the topic.

_ I’ve had worse _, Byleth had been quick to reassure their students, who hadn’t looked very reassured. 

“I would have waited,” Byleth says. “Half a year ago, I would have waited for back up. I wouldn’t have thought the risk of going into battle so undermanned and under-prepared worth it.”

Jeralt raises a brow. “So? Why did you?”

“I don’t know.” Byleth frowns. “I suppose I thought there could have been danger of Flayn being moved, now that we’d figured Jeritza out, but we didn’t even know for sure that Flayn was down there. The risk, technically, outweighed the reward, in that moment.”

“But you still took it,” Jeralt says, after a long moment of silence.

Byleth stares down at their hands; just the day before, they’d suffered happily through the pink Golden Deer girl painting their nails in pastel a shade lighter than her hair - and now half of those nails are broken, blood dried and flaking between each knuckle. “Yes,” they say, subdued. “I still took it.”

There’s a lot Jeralt could ask about. There’s a lot Jeralt _ wants _ to ask about - the spooked looks Seteth had shot his child before disappearing to his chambers with Flayn in his arms, the girl in a tattered Black Eagles uniform with hair the colour of blood that they’d also dragged out of that hellhole, that just a glimpse of had turned Hanneman the colour of whey.

Instead, he reaches out, and places a hand on Byleth’s head.

“You did good, kid,” he says. “I’m proud of you.”

Byleth’s answering smile is tiny, wavering, and uncertain, but to him, it’s the brightest thing in all the world.

The questions will keep for another day.


End file.
